[adamsilverstein]

Claude handled the version bump and wrote up the details:

Updates the bundled MediaElement.js library from 4.2.17 to the latest release, 7.1.0, and reviews the WordPress integration for compatibility.

Trac ticket: https://core.trac.wordpress.org/ticket/56320

What changed

• Vendor files updated to the 7.1.0 build from npm: mediaelement-and-player.js, mediaelement.js, the player stylesheets, mejs-controls.svg, and the Vimeo renderer. The YouTube, DASH, and HLS renderers remain part of the main bundle, so no new files are needed for those.
• Registered script and style versions in script-loader.php bumped from 4.2.17 to 7.1.0 so browsers cache-bust the new files.
• iconSprite added to the localized _wpmejsSettings - since MediaElement.js 5.0 the control icons are referenced from an SVG sprite, and without this setting players fall back to a page-relative path and icons fail to load.
• mediaelement-migrate.js gains one new shim: since 7.0, MediaElementPlayer.prototype.remove() no longer deletes the destroyed player from the mejs.players registry. WordPress iterates that registry (wp.media.mixin.removeAllPlayers(), mce-view, and wp-playlist re-creates a player per track change), so the shim restores the pre-7.0 cleanup.
• One existing migrate shim is corrected: it converted player.container, player.controls, and player.layers to jQuery objects for 4.x back compat, but 7.x internals call native DOM methods on them - setResponsiveMode() calls container.querySelector() for percentage-width players, which is exactly how [playlist] renders. Player construction threw and playlists could not switch or play tracks. The properties now stay HTML elements, with jQuery wrappers exposed as player.$container, player.$controls, and player.$layers instead. Core itself only calls container.remove(), which works natively.
• The favicon.ico that slipped in from the npm package build directory was removed.

Compatibility review

Every mejs API WordPress touches was checked against the 7.1.0 build: window.mejs, mejs.players, mejs.Utils.getTypeFromFile, mejs.Features, the mejsL10n i18n hook, the jQuery .mediaelementplayer() plugin, MediaElementPlayer and the prototype methods used by media-audiovideo.js, wp-playlist.js, and the customizer (remove, pause, globalBind/globalUnbind, getElement, buildfeatures, _meReady). The new 7.1.0 keyboard bindings go through player.getElement(), which the migrate shim's jQuery unwrapping already handles, and the default features list is unchanged, so the shim's buildfeatures override has not drifted. The 7.0.5 to 7.1.0 delta upstream is accessibility additions (keyboard play/pause, screen reader text for time/duration) and fullscreen fixes - no API changes.

Tests

• New QUnit module (tests/qunit/wp-includes/js/mediaelement.js) exercising the API surface above, including a functional check that instantiating a player builds its controls from the configured iconSprite and that remove() unregisters the player, plus a fluid-width player test covering the responsive sizing path. The QUnit page now also loads mediaelement-migrate.js in the same order production does. This test is what caught the mejs.players registry regression.
• New PHPUnit tests (tests/phpunit/tests/dependencies/mediaelement.php) that read the bundled library version out of mediaelement-and-player.js and assert every registered mediaelement script and style version matches it - so the files can no longer be updated without bumping the registered versions - and that the localized settings carry a resolvable iconSprite path.
• New e2e tests (tests/e2e/specs/media-playback.test.js) - the first front-end playback coverage in core. Each test publishes a post over REST and drives the real player in the browser: [audio] and [video] shortcodes (play, pause, SVG sprite controls, mejs.players registry), [playlist] audio track switching, [playlist type="video"], and the YouTube and Vimeo renderers (asserting their embed iframes attach). Playback assertions use mp3 and webm fixtures because Playwright's Chromium lacks proprietary codecs. The playlist test is what surfaced the responsive-mode fix above - playlists are the one core surface rendering a percentage-width player, and neither core nor Gutenberg had any test exercising these players before.

The QUnit suite (601 tests), the 6 PHPUnit tests, and the full e2e suite pass locally.

Testing Instructions

AI Use

Code, tests, and description all written with 🤖 Claude Code. I will review and test.

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